The long term goal of this project is to determine at a molecular level how recognition of unique oligosaccharide ligands by highly specific receptors modulate both the in vivo activity of secrete glycoproteins and cellular interactions via membrane glycoproteins. We have identified a new carbohydrate binding receptor motif that recognizes oligosaccharide with the terminal sequence S04-4-GalNAcbetal, 4GlcNAcbeta1, 2Man (S4GGnM) present on a limited number of membrane and secreted glycoproteins such as the reproductive hormone LH. The S4GGnM binding site is located in the N-terminal Cysteine-Rich domain of what was considered primarily a macrophage "mannose" (Man) specific receptor that also has 8 carbohydrate recognition domains (CRD's). The Man/S4GGnM-Receptor exists in two forms that bind to either S4GGnM- or to Man-bearing ligands. Thus both the specificity and the expression of this receptor are regulated in a cell specific manner. We have shown the S4GGnM-binding form of the receptor plays a critical role in reproduction by controlling LH circuitry half life. The presence of the Man/S4ggNm-Receptor in sperm-supporting Sertoli cells, and in lymph node and spleen macrophages that are adjacent to cells expressing S4GGnM- containing ligands at their surface, suggests this receptor also plays a role in inter-cellular communication. 1) We will determine the molecular basis for differential of S4GGnM- and Man-bearing ligands by this receptor using mutagenesis in combination with structural analysis by crystallography and nuclear magnetic resonance. 2) We will determine how the expression and specificity of the Man/S4GGnM-Receptor is regulated developmentally and hormonally in and characterized to determine if their expression is coordinately regulated with that of the receptor. 3) We will generate and characterize mice that are receptor deficient and determine the impact of the biology of glycoproteins bearing these unique structures. The Man/S4GGnM-Receptor is a versatile, multi- functional receptor. Its function in any given setting will reflect the cell type expressing the receptor, the specificity of the receptor, and the character of the glycoproteins bearing oligosaccharides that are recognized. Our studies will provide new insights into the biology of this complex system that plays important roles governing cell behavior during development, reproduction, and the immune response.